Meander line antenna coupler and shielded meander line

ABSTRACT

A switched meander line structure is substituted for a lumped element antenna tuner for an order of magnitude increase in gain due to the use of the switched meander line architecture. The use of the meander line with relatively wide and thick folded legs markedly decreases I 2 R losses over wire inductors whose wire diameters at one-tenth of an inch contribute significantly to I 2 R losses. Additionally, placing solid state switches to short out various sections of a multi-leg meander line at high impedance nodes reduces I 2 R losses across the switching elements in the tuner.

This application is a 371 of PCT/US03/34996 filed on Nov. 3, 2003, whichis a continuation of U.S. application Ser. No. 10/378,336 filed on Mar.03, 2003 now U.S. Pat. No. 6,894,656 which claims priority of U.S.Provisional Application Ser. No. 60/435,099, filed Dec. 20, 2002.

FIELD OF THE INVENTION

This invention relates to antenna couplers and more particularly both tothe utilization of a meander line architecture for providing the couplerand to a shielded meander line.

BACKGROUND OF THE INVENTION

Lumped element antenna couplers have been used in the past toefficiently couple energy into antennas whose impedance is not matchedwith that of the transmission line. Typically, transmission lines are50-ohm devices and when using, for instance, whip or monopole antennas,these antennas typically have impedances at the base of the antenna atabout 0.05 ohm in the high frequency or HF band. When the transmissionline is matched to the impedance at the base of the antenna, the couplerlimits the energy dissipated in resistive losses and maximizes thetransmitted energy. so that the antenna can be easily excited andoperated at or near resonance.

Thus, antenna couplers for monopole antennas are able to match theimpedance at the feed of the antenna with that of the transmission lineby raising its relatively low impedance to that of 50 ohms.

Moreover, not only does one have 0.05 ohms at the base of a whip ormonopole, one has a relatively large reactance which must be canceledout for efficient transfer of energy from the signal source to theantenna. While the large reactance might typically be canceled out usinga loading coil to cancel out the capacitive reactance, one nonethelesshas to match whatever resistance is left to the 50-ohm impedance of thetransmission line.

Typical antenna couplers in the past involving lumped elements includecombinations of inductors and capacitors in either a T network or a pinetwork configuration. In order to change the inductance or capacitanceso that the impedance at the feed of the antenna is matched to theimpedance of the transmission line, originally inductors weremechanically tapped along their coils or capacitors were provided withvariable capacitance plates. The inductance and the capacitance werevaried mechanically in order to match antenna impedance to the impedanceof the transmission line. However, for frequency-hopping applications inwhich the frequency of the source is switched in microseconds, it becamenecessary to utilize solid state switching in order to switch in or outvarious taps of a coil or in order to switch various capacitors in andout in time to accommodate the frequency change.

Problem with the utilization of such lumped elements center around I²Rohmic heating losses which result either from the relative thinness ofthe wire utilized in the inductors or internal resistance of the solidstate switches. Moreover, since the solid state switching utilized inthese couplers was placed at high-current nodes, oversized and expensiveswitches were required.

Thus, while mechanical switching was suitable some 40 years ago forantenna couplers, with the advent of frequency-hopping, it is too slow.There was therefore a need for rapid re-tuning of antenna couplers thatrequired the use of solid state switching.

Regardless of whether solid state switches were used, the prior lumpedelement couplers resulted in I²R losses that in turn resulted in a 20 to30 dB reduction in radiated power.

Since large amounts of power are lost in the inductors and the diodeswitches that switch in and out the capacitors and inductors, onerequires a much more efficient coupling system. The ohmic losses areprimarily due to the circulating currents in the elements that can riseto huge values to cause the high I²R ohmic losses. The only way onecould reduce these losses with conventional lumped element couplers isto make the inductors and capacitors very big. One would therefore haveto have a container that was perhaps three feet by three feet by threefeet in order to attempt to limit the, ohmic losses. However, as onemakes the inductors large, the Qs get too high, which results inextremely high voltages and even greater ohmic losses. Additionally,with the very high voltages involved with the large components, thediodes that are utilized in the solid state switching are heavilystressed. Thus, solid state switches for these larger units would haveto be extremely massive and expensive.

For a reasonably-sized lumped element coupler operating, for instance,at 2 megahertz and feeding, for instance, a loop antenna having asix-foot radius corresponding to a whip on the back of the truck whichhas its tip bent and attached to the forward end of the truck, gainshave been measured at −23 dBi. This means that a considerable amount ofthe power which should be coupled to the antenna is lost as heat in theantenna coupler. As will be seen hereinafter, substituting a switchedmeander line architecture for the lumped element coupler results in a−13 dBi overall gain, which is an improvement of 10 dB over the lumpedelement coupler. This corresponds-to an order of magnitude improvement.

SUMMARY OF INVENTION

Rather than utilizing a lumped element coupler, in the subject inventiona meander line is substituted for the coupler. The meander line is along, slow wave delay line folded on itself, with the diode switchesbeing interposed to switch transmission line sections in and out toobtain the proper length for the matching of an arbitrary antenna to aparticular transmission line impedance.

Typically, the folded sections of the meander line are made out ofcopper strips which may be one inch wide by one-tenth inch thick. Theuse of so much metal results in much less ohmic loss as compared with,for instance, Number 12 wire typically utilized in inductors for lumpedelement couplers.

Moreover, the circulating currents in the meander line are not verylarge so one does not have a lot of ohmic loss as compared with theohmic loss associated with an inductor.

In one embodiment, the switching is made to occur at the high impedancepoints for the meander line so that very little current flows throughthe diode switches. This also limits the I²R losses.

It is a finding of this invention that regardless of the impedance ofthe antenna at its feed point, there are combinations of meander linesegments that may be switched in and out to tailor the resistance andreactance of the meander line so that when it is coupled in parallel tothe antenna resistance and reactance an antenna input impedance iscreated that matches the impedance of the transmission line.

Originally, it was not clear that any combination of meander line legscould be introduced that would match an arbitrary antenna impedance to aparticular transmission line impedance. However, after experimentationit was found that, by switching in and out various segments of meanderline, one could in fact match any arbitrary impedance to the impedanceof the transmission line. The reason, it was found, is that theyet-to-be-determined input impedance of the antenna is proportional tothe ratio of the square of the sum of the capacitive reactances of themeander line over the unloaded Q of the meander line. With the VSWRcalculated, it was found that the total capacitive reactance decreaseswith frequency in synchronism with the unloaded Q of the meander line.This property accounts for the ability to maintain a good match overfrequency as the meander line is tuned to achieve resonance by shortingout combinations of its sections.

As a result, the outstanding characteristic of the meander line-loadedantenna used as a coupler is that near the resonant frequency, thecurrent distribution along its vertical and horizontal plates is highlypeaked at the gap between the vertical and the horizontal plates. Thegap region was found to harbor a parallel resonance formed by themeander line and the distributed capacitance between the horizontal andvertical plates and the impedance of the antenna, namely R_(A), X_(A).Thus, the meander line exhibited a parallel resonance effect. As aresult, by coupling the meander line in parallel with the resistive andcapacitance impedance of the antenna, one could tailor the impedance ofthe antenna input to match that of the transmission line.

Note that the slow wave meander line loaded antennas have been describedbefore and are characterized in U.S. Pat. No. 5,790,080 incorporatedherein by reference. This patent describes an antenna that includes oneor more conductive elements acting as radiating antenna elements and aslow wave meander line adapted to couple electrical signals between theconductive elements. The meander line has an effective electrical lengththat affects the electrical length and operating characteristics of theantenna.

Meander lines are routinely connected between the vertical andhorizontal conductors at a gap, with the meander line slow wavestructure permitting lengths of meander line to be switched in or out ofthe circuit quickly and with negligible loss. In part, this switching ismade possible because active switching devices are located athigh-impedance sections of the meander line. This feature keeps thecurrent through the switching devices low and results in very lowdissipation losses in the switch, thereby maintaining high antennaefficiency.

The meander line loaded antenna allows the physical antenna dimension tobe reduced significantly while maintaining an electrical length that isstill a multiple of a quarter wavelength of the operating frequency.

U.S. Pat. No. 6,325,814 for wide band meander line loaded antennas isalso included herein by reference. This reference discloses a meanderline loaded antenna which provides a wide instantaneous bandwidth. Afirst planner conductor is substantially parallel to a ground plane andis separated from the first planner conductor by a gap, with the meanderline interconnecting the first and second planner conductors.

Having described the existing meander line loaded antennas, it is theobject of the present application to substitute a switched meander linefor a lumped element antenna coupler, with the switched meander lineconstituting a variable-impedance transmission line. While balun coilshave been utilized in the past to match antennas to transmission lines,the balun coils are not able to match an arbitrary impedance.

The purpose of the switched meander line in the subject invention is totake the antenna impedance and the meander line impedance and connectthem in parallel, and then alter the impedance of the meander line sothat the parallel combination of the two impedances provides a pointthat matches a predetermined transmission line impedance, such as 50ohms. For any given frequency, it has been found that the parallelcombination of the meander line impedance and the antenna impedance canbe made to match the transmission line impedance and that, by adjustingthe impedance of the meander line through the above-noted switching, onecan always find a suitable match.

As will be further seen, it is possible to provide the meander linestructure with a shield which, in addition to decreasing the lowfrequency cutoff of the device, also results in various sections of themeander line being high-impedance nodes at which one can place solidstate diode switches, with the high-impedance nodes carrying virtuallyno current. The result is that one can fabricate an antenna coupler withrelatively inexpensive solid state switches. Moreover, since I²R lossesare minimized because of the heavy meander line elements and the lowinternal resistance of the switches, the meander line architectureprovides an order of magnitude improvement in gain over lumped elementcouplers.

In summary, a switched meander line structure is substituted for alumped element coupler for an order of magnitude increase in gain due tothe use of the switched meander line architecture. The use of themeander line with relatively wide and thick folded legs markedlydecreases I²R losses over wire inductors whose wire diameters contributesignificantly to I²R losses. Additionally, placing solid state switchesto short out various sections of a multi-leg meander line at highimpedance nodes reduces I²R losses across the switching elements aswell. It has been found that, regardless of the impedance of theantenna, this impedance may be matched by switching in and out varioussections of a folded multi-leg meander line due to the fact that thesquare of the sum of the capacitive reactances of the meander linedecreases with frequency in synchronism with the unloaded Q of themeander line, thus to provide the ability to maintain a good match overfrequency as the meander line is tuned to achieve resonance by shortingout combinations of sections of the meander line. The result of thesubstitution of the meander line architecture for the lumped elementcoupler is the reduction of losses associated with the use of wireinductors and losses due to the interposition of solid state switches athigh-current nodes.

Shielded Meander lines

More specifically and by way of further background, slow wave meanderline loaded antennas are known, with the meander line providing for anarrow band and a wide band response, depending on the application. Onepatent describing such a slow wave meander line structure is U.S. Pat.No. 6,313,716 assigned to the assignee hereof and incorporated herein byreference. In this meander line embodiment, the meander line includes anelectrically conductive plate, and a plurality of transmission linesections supported with respect to the conductive plate. The pluralityof sections includes a first section loaded relatively closer andparallel to the conductive plate to have a relatively lowercharacteristic impedance with the conductive plate, and a second sectionlocated parallel to and at a relatively greater distance from theconductive plate than the first section to have a relatively highercharacteristic impedance with the conductive plate. A conductor isprovided for interconnecting the first and second sections andmaintaining an impedance mismatch therebetween.

If one were to use the above meander line in a coupler in someapplications one could use a wider band response in terms of decreasedfrequency cutoff. While meander lines are used to provide a compact orminiaturized device no matter what the frequency band, for each bandobtaining a lower frequency cutoff is often important.

For instance, for low frequency communication in which a grounded loopantenna replaces the traditional whip antenna mounted to a vehicle, theability to operate down to 4 MHz is vitally important. The low frequencyrequirement is to assure close-in sky wave communications by having thetake-off angle as steep as possible. However, getting the meander lineantenna coupler described above to operate at 4 MHz can be challenging.Either meander line couplers have to double their footprint or theantenna has to be elongated and may extend up too far, meaning it canget caught on trees or overhanging vegetation, to say nothing of lowlying power or telephone lines.

Moreover, as described above, meander line couplers have various meanderline sections switched in and out to change the frequency at which themeander line is tuned. Because the PIN diode or FET switches can beplaced between a high impedance section of the meander line and a lowimpedance section, the open switch differential voltage across theswitch may be in excess of 10,000 volts. This causes substantial voltagestress that can cause the switches to fail, which in turn limits thetransmit power allowed so as not to burn out the switches. While in atactical situation one might want to switch from 100 watts to 300 watts,switch failure would prevent one from so doing.

Going from military to civilian use, for the cellular and PCS bands itis important to provide a miniature wide band antenna that can operatebetween 800 and 3,000 MHz. Unfortunately it is only with difficulty thatone can get below 1500 MHz using standard meander line loaded antennas.In short, for standard meander line loaded antennas there is a severelow frequency threshold. This limits how low a cutoff frequency for themeander line can be. What is needed is a breakthrough in the lowfrequency cutoff of meander line loaded antennas for such applications.

A third application is for military communications in the 30–88 MHzband. What is required is a reduced footprint antenna that is smallenough to be carried on a vehicle or aircraft and yet operate in the30–88 MHz band. Standard meander line loaded antennas, while small, arenonetheless too large at 30 MHz. Again, what is needed is a breakthroughin the lowering of the low frequency cutoff for meander line structuresin the 30–88 MHz range so that a suitably sized device will work.

Whether it be for 4 MHz communications, 30 MHz communications or 800+MHz communications, there is a need for a compact device having areduced the low frequency cutoff. Note that a standard meander linecoupler at 4 MHz would have a footprint of 28″×50″, inconvenient to beplaced on the top of a small vehicle. For the 30–88 MHz range a meanderline loaded antenna would have to be as large as 16″×48″×48″, againinconvenient for vehicle or aircraft use. In the cellular and PCSapplications, meander line loaded antennas are only 0.3″ high×1.2″wide×1.2″ long. However, their low frequency cutoff is approximately1500 MHz, too far above the cellular 800 MHz band.

What is therefore necessary is a new meander line configuration todramatically lower the low frequency cutoff of such devices.

By way of further background, for military use, taking a tacticalsituation in which a soldier or vehicle needs to communicate withanother soldier or vehicle at some distance away, typicallycommunications is provided through the use of a ground wave and alsofrom skip off the ionospheric layer. While a ground wave is usuallyviable up to about 30 miles from the transmission site, if the skipangle is shallow, there will be a significant blackout or dead zonealong the ground, say from 30 miles to 100 miles, where there will be nocommunications possible. This is because the transmitted radiation skipsover this ground segment before it is reflected down to the surface ofthe earth.

When depending on a sky wave or a skip for robust communications, thetakeoff angle of the radiation is indeed important. It is noted that thehigher the frequency the more shallow is the takeoff angle such thatthere is more of an extended dead zone which starts at the transmissionsite and extends to the point at which radiation reflected from theionosphere strikes the surface of the earth. This means that there is acommunications blackout zone, for instance, between 30 miles and 100miles when a transmitter is operating in the 5 MHz frequency band. Thisis because of the somewhat shallow takeoff angle in which no radiationfrom the transmitter reaches a position on the surface of the earthbeyond the point at which the ground wave dissipates. Thus in the aboveexample, there would be no communication possible between 30 miles and100 miles from the transmitter.

Were it possible to be able to lower the operating frequency of thetransmitter to, for instance, 4 MHz, then the takeoff angle would behigher and radiation returned from the ionosphere would be closer to thetransmitter, e.g. between 30–100 miles: of the transmitter. What thismeans is that communications could established from the transmitter allthe way up to the 30 mile limit of the ground wave transmission and thenup to another 100 miles due to the sharper skip angle involved withoperating at the lower frequency.

While it is certainly possible with a long whip antenna to be able totransmit at 4 Mz, it would be desirable to be able to use a shortradiator and a meander line structure as a miniature coupler to permitoperating at 4 MHz. Thus, rather than having to have a quarter waveantenna at 4 MHz, one needs to find how to construct a miniaturizedcoupler for a very short length whip or loop. One therefore needs todevelop a meander line coupling device that without enlarging the devicewould lower the VSWR to less than 2:1 at the lower frequency. This wouldpermit a continuum in the communications capabilities of the transmitterwhile at the same time using a smaller radiator and the sameminiaturized meander line coupler.

For 30–88 MHz use, this is a frequency hopping communications band usedextensively by the military. The antenna structures for this band aresizeable and there is a need to be able to reduce the size of theantenna structures so that they can be readily mounted to vehicles oraircraft. While meander line couplers and antennas have been proposedfor such use, they cannot be made to operate close to 30 MHz, at leastat sizes that are required. To make such an antenna operate at 30 MHzthe size required is a volume 16″ high×48″ wide×48″ long, or 36,864cubic inches. This resulted in rejection of such antennas for tanks andsome aircraft. If one could design a wideband antenna for this band at10″×32″×32″ or 10,240 cubic inches, then there is enough real estate onthe vehicle due to a volume reduction of 3.7:1.

Another antenna related problem is one that is typical of cell phoneantennas. First, one needs a compact wideband antenna that can cover thecellular band at 800 MHz, and the PCS bands at 1.7–1.9 GHz, as well asoperating at the GPS frequency of 1.575 GHz. Getting a meander lineloaded antenna to operate down to 800 MHz at the current size requiredis a challenge.

Moreover, there is another problem that needs to be resolved withwideband cellular antennas. Since most cell phone antennas are backedwith a ground plane, usually the ground plane of the printed circuitboard within the cell phone, there is a problem called “down firing”, inwhich the major lobe of the antenna points into the ground. This limitsthe ability of the hand held device both in the receive and in thetransmit mode because radiation transmitted from such a device is firedinto the ground, whereas the receive characteristic is diminished in thehorizontal direction. While meander line loaded antennas have been usedin cell phones because of their small size and wide bandwidth operatingin the 800 MHz, 1.7 GHz and 1.9 GHz bands, they nonetheless suffer from“down firing” at frequencies above 1.7 GHz. It would be convenient ifsome meander line structure could also eliminate the down firingproblem.

As part of the subject invention, a standard slow wave meander linestructure is provided with a top shield. This has a number of importanteffects. First, the resonant frequency of the device is significantlylowered, which means that its low frequency cutoff is likewise lowered.Secondly, the effective radiation pattern of a meander line loadedantenna has a major horizontal lobe unaffected by ground planes in awireless device regardless of operating frequency, thus to eliminatedown firing. Thirdly, if one wishes to have a frequency switched meanderline structure, voltage stress on the switches can be reduced.

As defined herein, a modified slow wave meander line structure that canbe used as a coupling mechanism for 4 MHz transmissions withoutincreasing its size, can be used as a wideband antenna for the 30–88 MHzapplications, and can be used as a wideband cell phone antenna having alow cutoff frequency down to 800 MHz. The modified slow wave meanderline structure also eliminates the ground plane “down firing” problemand eliminates switch stress in frequency switched meander lines.

Shield Structure

To do this, a standard meander line structure having a conductor plateis provided with a top shield over the structure, with the shield beingcoupled to the conductor plate. The top shield lowers the operatingfrequency of a meander line by affecting the propagation constant of themeander line structure. The propagation constant relies on the number ofhigh impedance/low impedance transitions per unit length. Thischaracteristic is the result of the fact that each transition causes afixed phase shift. The more phase shift per unit length, the more delayper unit length. When utilizing a top shield connected to the conductorplane, there are more phase shifts per unit length and therefore moredelays per unit length. Put another way, with the same size meander linestructure, its effective length is increased which lowers its operatingfrequency. The top shield thus provides a double-sided device that hasdouble the number of transitions per unit length such that more delay isaccrued.

What in essence is happening with the use of the top shield is that itturns what was a low impedance section between two high impedancesections into a high impedance section between two low impedancesections thus, when utilizing the top. shield, the high impedancesections are now the vertical segments or sections of the meander line.The horizontal sections become the low impedance sections. If switchesare put in these high impedance sections to switch the operatingfrequency of the meander line, then the switching stress is reduced.This means that the voltage differential across the switch is muchdecreased, it being from one low impedance section to another lowimpedance section. Thus, with the top shield an added advantage is thathigher power communications can be achieved without switch burn out.

In order to provide such a dramatic break through it has been found thatproviding a grounded shield over this standard meander line structuresignificantly reduces the low frequency cutoff of the device withoutaltering its size. The shield does so by changing the high/low impedancesections to one where the high impedance section is between two lowimpedance sections. Also, any switching is now done between two lowimpedance sections which drastically reduces voltage stress.

In one embodiment, the unshielded meander line when used as a couplerhas a resonant frequency of 5.2 MHz, while the shielded meander has aresonant frequency of 4.05 MHz.

In summary, a standard slow wave meander line having sections ofalternating impedance relative to a conductor plate can be provided witha top shield connected to the conductor plane for the purpose oflowering the resonant frequency of narrow band antennas and lowering thelow frequency cutoff limit of wide band antennas. This is due to ahigher delay per unit length occasioned by the use of the top shield.

The shielded meander line may be utilized as a coupling device totruncated antennas such as a whip antenna or grounded loop antenna forthe purposes of loading the antenna so as to provide lower frequencyperformance. Since the propagation constant of the meander linestructure depends upon the number of high impedance/low impedancetransitions per unit length, the utilization of the top shield resultsin more phase shifts per unit length and thus more delay per unitlength, with the symmetric double sided version having double the numberof transitions per unit length. When configured to provide a miniatureantenna for use in wireless handsets, the utilization of the top shieldboth lowers the cutoff frequency and eliminates down firing typical ofwireless phone antennas due to the ground plane effect. Moreover, thetop shield provides a uniform low VSWR over wide bandwidths and byvirtue of lowering the operating frequency solves a skip-inducedblackout problem due to the lower frequencies that can now be used.Further, for frequency switched meander lines, voltage stress is reducedby using the top shield. Finally, reducing the volume requirement byover 30% permits mobile use where real estate is at a premium.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the subject invention will be betterunderstood in connection with a Detailed Description, in conjunctionwith the Drawings, of which:

FIG. 1 is a block diagram of a prior art lumped element coupler,coupling a monopole antenna to a signal source;

FIG. 2A is a schematic illustration of the subject meander line antennacoupler showing the meander line coupled to a monopole antenna, alsoillustrating the capacitance between the top plate and ground and theimpedance of the antenna across the gap;

FIG. 2B is a equivalent circuit for the couple of FIG. 2A illustratingthe parallel connection of the meander line impedance with the antennaimpedance so as to present an adjusted antenna input impedance to thetransmission line;

FIG. 3A is a schematic diagram of the subject meander line antennacoupler showing the meander line coupled to a loop antenna, showing oneend of the loop coupled to the signal source side of the meander line;

FIG. 3B is an equivalent circuit for the couple of FIG. 3A showing theparallel connection of the meander line impedance with the antennaimpedance, also illustrating the connection of one end of the loop tothe signal source side of the meander line;

FIG. 4 is a diagrammatic illustration of the subject antenna coupler,showing a series of folds in a meander line with shorting switches oropening switches at various points in the folded meander line structureso as to be able to switch in and out various segments of the meanderline;

FIG. 5 is a diagrammatic illustration of one embodiment of a foldedmeander line structure capable of being adapted for antenna coupler use;

FIG. 6 is diagrammatic illustration of one segment of the meander lineof FIG. 5, showing the interposition of a number of solid state switchesto short out and to connect various sections of the meander line legtogether;

FIG. 7 is a diagrammatic illustration of the use of a standard meanderline structure as a coupler to a grounded loop antenna;

FIG. 8A is an isometric and schematic illustration of a shielded meanderline structure illustrating the top shield;

FIG. 8B is a schematic diagram of the meander line structure of FIG. 2A,showing the electrical connection of the top shield to the conductorplate of the meander line;

FIG. 9A is a waveform diagram illustrating the high and low impedanceportions of a meander line structure;

FIG. 9B is a schematic diagram of the interposition of a switch in thevertical transition between the high and low impedance sections of themeander line of FIG. 1 to be able to switch the operating frequency ofthe meander line, illustrating the high voltage stress on the switch dueto the high to low impedance transition;

FIG. 10A is a waveform diagram of the result of providing a top shieldon the impedance of the meander line segments illustrating a lowimpedance sector couple to another low impedance section through avertical high impedance section, thus to double the number of impedancetransitions. for a given length meander line;

FIG. 10B is a schematic diagram of the interposition of a switch in thevertical high impedance transition between the low impedance sections ofthe meander line of FIG. 1 to be able to switch the operating frequencyof the meander line, illustrating the a significant reduction in thevoltage stress on the switch due to the low to low impedance transition;

FIG. 11 is a diagrammatic illustration of a multiple section meanderline used as a coupler to a grounded loop antenna;

FIG. 12 is a diagrammatic illustration of the multiple section meanderline coupler of FIG. 11, illustrating the use of a top shield to lowerthe low frequency cutoff of the meander line;

FIG. 13 is a diagrammatic illustration of a skip transmission scenarioshowing the effect of lowering the frequency of the transmission toeliminate a dead zone by increasing the take-off angle which decreasesthe skip distance;

FIG. 14 is a waveform diagram of a compact meander line loaded antenna.operating in the 30–88 MHz band illustrating the VSWR with and withoutthe use of a top shield;

FIG. 15 is a diagrammatic illustration of the volume occupied by ameander line loaded antenna operating in the 30–88 MHz band illustratingthe effect of using a top shield to reduce the volume to 10,000 squareinches;

FIG. 16A is a schematic diagram of a meander line loaded antenna with atop shield for use as a wideband device for use in wireless handheldcommunications in which the top shield lowers the low frequency cutoffbelow the cellular band;

FIG. 16B is a waveform diagram illustrating the VSWR for the topshielded meander line loaded antenna of FIG. 10A, comparing it to theVSWR of an unshielded meander line loaded antenna of the same size;

FIG. 17 is a diagrammatic illustration of the antenna lobe pattern foran internally carried antenna in a wireless handset for use in the 800MHz band;

FIG. 18 is a diagrammatic illustration of the antenna pattern of aninternally carried wireless handset antenna in the 1.9 GHz band showinga down firing pattern due to the ground plane effect caused by theground plane of the printed circuit board or boards used in the wirelesshandset;

FIG. 19 is a diagrammatic illustration of the lobe structure for ameander line loaded antenna embedded into a wireless handset operatingin the 800 MHz band; and,

FIG. 20 is a diagrammatic illustration the antenna lobe pattern for anembedded meander line loaded antenna at 1.9 GHz having a top shieldwhich eliminates any down firing ground plane effect.

DETAILED DESCRIPTION

Referring now to FIG. 1, a conventional lumped element coupler 10 iscoupled between a monopole or whip antenna 12 and a signal source 14coupled between the coupler and ground. As mentioned hereinbefore,whether the lumped element coupler involves pi networks or T networks,each of these networks involves discrete elements in the form of acoiled inductor and a capacitor. Typically, the lumped element couplersact by changing the inductance or capacitance to match the impedance ofthe antenna to a particular transmission line, here shown at 16. In thecase of inductors, the inductors are tapped at various points eithermechanically or through switching circuits, whereas the capacitors maybe made variable either. by a variable plate or by switching in and outa number of capacitors to provide for the appropriate coupling of theantenna to the transmission line.

Rather than utilizing a lumped element coupler and referring now to FIG.2A, what is shown is the use of a meander line 20 as an antenna couplerwhich is interposed between a signal source 22 and a monopole or whipantenna 24. The meander line in one embodiment has switched sectionsthat enable it to vary its impedance which, when coupled in parallelwith the impedance of the antenna, are such as to match the impedance atthe base of the whip or monopole with the impedance of transmission line26.

As illustrated schematically, meander line 20 is composed of a number offolded legs or sections 28 and 30, joined by an upstanding portion 32,with the meander line exhibiting a slow wave function due to thediscontinuities and the impedances of the meander line. The meander linehas a ground plate 34 to which one side of signal source 22 is coupled,and a top plate 36, as illustrated. It is noted that the base of antenna24 is connected to the meander line at a point 38, which is the junctureof an upstanding portion 40 of meander line 20 and top plate 36.

As illustrated, there is a capacitance between top plate 36 and ground,as illustrated by C, whereas the impedance of the antenna at point 38 isillustrated by a resistive component, R_(A), and a reactance component,illustrated by X_(A).

Referring to FIG. 2B, the equivalent circuit for the meander linecoupler and antenna of FIG. 2A indicates that there is a voltage sourceto ground at 42 coupled to the junction of parallel connected impedancesformed by R_(L) and X_(L) for the meander line and R_(A) and X_(A) forthe antenna. The capacitance of the top plate to ground C is as noted.

As will be described hereinafter in rigorous detail, it has been foundthat the. meander line segments can be connected together in such a waythat R_(L) and X_(L), when connected in parallel with R_(A) and X_(A),result in an impedance at point 50 which matches the impedance oftransmission line 26.

Referring to FIG. 3A, in this case a loop antenna 52 is coupled betweena point 54 and ground, with point 54 being the distal end of meanderline leg or section 30, with like reference characters referring to likecomponents between FIGS. 2 and 3. It will be noted that the differencebetween the connection of the meander line coupler in FIGS. 2 and 3 isthat for monopole or vertical antennas therein bases are coupled atpoint 38, whereas four loop antennas, one end of the loop is coupled atpoint 54.

Again with respect to the loop antenna and referring now to FIG. 3B, themeander line impedance composed of R_(L) and X_(I), is effectivelyconnected in parallel to the impedance at the input of the antenna,namely R_(A) and X_(A), such that, for a variable length meander line,the meander line impedance in parallel with the antenna input impedanceat point 54 can be made to match that of the transmission line. It isnoted that the impedance of the normal coaxial transmission line used is50 ohms.

Referring to FIG. 4, how the impedance of the meander line is changed oraltered is shown through the utilization of solid state switches 60interposed between folded portions 62 and 64 of various adjacent meanderline segments. By virtue of closing or opening of these switches,various lengths of meander line are connected between antenna 24 andsource 22, with the length of meander line corresponding to a variablelength transmission line utilized in matching antenna 24 to transmissionline 26.

These switches are typically solid state and under the control of acircuit 66 that is programmed to selectively activate certain of theseswitches to control the effective length of the meander line and itsimpedance.

In general, the use of the meander line results in relatively lowcurrents existing within the meander line such that the switchesthemselves may not be as robust as, for instance, those switches thatare utilized in lumped element couplers. Moreover, as illustrated byswitches 60′, one can locate theses switches at the high impedance lowcurrent nodes between the low impedance sections of the meander line soas to connect together various sections of the meander line withoutsuffering loss through the switch.

Referring to FIG. 5, a typical meander line suitable for use as acoupler includes a number of folded sections. Here a top section 72meets a lower section 74, which is in turn coupled via a couplingconductor 75 to a lower section 76 of an adjacent meander line section.This section is in turn coupled to an upper portion 78 which is in turncoupled via a conductor 79 to a lower portion 80, in turn coupled to anupper portion 82. It will be noted that the upper and lower portions inone embodiment are made out of copper which is a tenth of an inch thickand which is one inch wide. The result is that, for these type ofmeander lines, there is very little resistance and therefore exceedinglylow ohmic loss. It is noted that each of the folded sections lies on itsown insulator 73 atop a ground plate 75. The connections to the meanderline are illustrated at 84 and 86.

Referring now to FIG. 6, a portion of the meander line of FIG. 5 isillustrated in which solid state switches 90, 92 and 94 are used tointerconnect various portions or segments of the folded meander line.Here, solid state switches 90 and 92 serve to short out the meander lineto foreshorten it at points 96 or points 98, whereas solid state switch94 connects together what is a high impedance node for the meander lineas illustrated by meander line sections 100 and 102 such that they areconnected together by switch 94 at points 104 and 106.

By way of further explanation, the meander line antenna coupler, whichincludes a variable impedance transmission line, makes optimum use ofthe physical volume enclosed by the structure. The meander line antennacoupler is capable of being tuned by adjusting the length of thevariable impedance transmission line. with switches.

As an example, an “L-shaped” meander line antenna coupler is the basicbuilding block used in creating more complex meander line antennacoupler based arrays. The outstanding characteristic of the meander lineantenna coupler is that near the resonant frequency, the currentdistribution along the vertical and horizontal plates is highly peakedat the gap. The gap region has been found to harbor a parallel resonanceformed by the meander line and the distributed capacitance between thehorizontal and vertical plates and the impedance of the external antennaR_(A), X_(A). Two different computer simulation codes (Sandia Tripatch,HFSS) have shown this characteristic.

It has been found that the meander line antenna coupler input impedanceis the sum of the gap region impedance and the capacitance of thehorizontal plate to ground. The meander line with its alternating highand low impedance sections is a fair approximation to a slow wave,non-dispersive transmission line with characteristic impedance equal tothe geometric mean of the high and low impedances. The gap region isrepresented by an impedance, Z, which is the parallel combination of a)the impedance seen at the gap without the meander line attached and b)the meander line equivalent non-radiating transmission line. Theimpedance at the gap, which is the combination of the external antennaand the gap region, is measured or calculated with the aforementionedsimulation codes. The capacitance of the horizontal plate isapproximated by calculating the self-capacitance of the plate andapplying a correction due to the proximity of the ground. The gapimpedance is measured with the meander line antenna coupler in proximitybut not directly connected to ground. Note that the meander line antennaequivalent circuit is valid only near resonance.

C is the horizontal plate capacity, R_(A) is the antenna radiationresistance, X_(A) is the antenna reactance, R_(L) is the loss resistancein the meander line and X_(L) is the reactance in the meander line.

The VSWR is low over the whole -tuning range, made possible because theinput resistance at resonance is proportional to X_(C) squared andinversely proportional to unloaded Q. As frequency increases thesequantities decrease at the about same rate, thus keeping the inputresistance constant. As will be shown, the exact form is:Ro=πX _(C)/²(4ZoQu)The meander line equivalent shorted line impedance is:

${Zml} = \frac{Zo}{\frac{R_{L}}{2{Zo}} - {{j/\tan}\;\beta\; L_{eff}}}$This is an approximation of a low loss shorted transmission line and isaccurate as long as tanβL_(eff) is much greater than R_(L)/2Zo. Zo isthe meander line impedance, _(Leff) is the effective length of the line,and β=ω/c.

The unloaded Q of the transmission line is

${Qu} = \frac{\pi\;{Zo}}{2R_{L}}$

The parallel combination of Zml and the antenna impedance R_(A)+j X_(A)gives rise to the impedance function of the gap region:

$\begin{matrix}{{Z = \frac{Zo}{\frac{Reff}{2{Zo}} - {{j/\tan}\;\beta\; L_{eff}} - {j\;{{Zo}/X_{A}}}}}{{{Where}\mspace{14mu}{Reff}} = {R_{L} + {2R_{A}{{Zo}^{2}/X_{A}^{2}}}}}{{Qu} = {\frac{\pi\;{Zo}}{2{Reff}}\mspace{14mu}{and}}}{{{MLA}\mspace{14mu}{efficiency}} = {\frac{2R_{A}\mspace{14mu}{Zo}^{2}}{{ReffX}_{A}^{2}}*{mismatch}\mspace{14mu}{loss}}}} & \left. 1 \right)\end{matrix}$Since one desires the impedance at the feed to be real, one sets thereal part of Z (equation 1) equal to Ro, the yet to be determined inputimpedance. This results in the expression1/TanBL _(eff) +Zo/X _(A) =SQRT[πZo/(4QuRo)]  2)The effective length of the meander line is determined by solvingequation 2) for tanβ L_(eff).

Inserting equation 2) in the expression for Z (equation 1), leads to theexpressionIMAG(Z)=Imaginary part of Z=SQRT(Qu Zo Ro4/π)

Setting IMAG(Z) to −X_(C), to cancel out the horizontal plate capacity,the following relation is arrived at:

${Ro} = \frac{X_{C}^{2}\pi}{4{ZoQu}}$The above equation enables the VSWR to be calculated. It is revelatoryto note that X_(C) decreases with frequency and is in synchronism withQu. This property accounts for the ability of the switched meander lineto maintain a good match over frequency as the meander line is tuned toachieve resonance by shorting out combinations of sections of themeander line regardless of the arbitrary antenna used.

Shielded Meander line

Referring now to FIG. 7 and as described in U.S. Pat. No. 6,313,716, aslow wave meander line structure 200 is in the form of a foldedtransmission line 222 mounted on a plate 224. Plate 224 is a conductiveplate, with transmission line 222 being optionally constructed from afolded microstrip line that includes alternating sections 226 and 227which are mounted close to and separated from plate 224, respectively.This variation in height from plate 224 of alternating sections 226 and227 gives these sections alternating impedance levels with respective toplate 224.

Sections 226, which are located close to plate 224 to form a lowercharacteristic impedance are electrically insulated from plate 224 byany suitable means such as an insulating material positionedtherebetween. Sections 227 are located at pre-determined distance fromplate 224, which predetermined distance determines the characteristicimpedance of transmission line section 227 in conjunction with the otherphysical characteristics of the line as well as the frequency of thesignal being transmitted over the line.

As illustrated, sections 226 and 227 are interconnected by sections 228of the microstrip line which are mounted in an orthogonal direction withrespective to plate 224. In this form the transmission line 222 may beconsidered as a single continuous folded microstrip line.

Note that one end of the meander line is illustrated by referencecharacter 220, whereas the other end of the meander line is illustratedby reference character 230. Moreover, in one embodiment end 230 iselectrically coupled to plate 224 as illustrated at 232.

In one embodiment, end 220 of the meander line may be connected to agrounded loop radiating element 234. This loop is grounded at one end,with the combination providing a narrow band antenna arrangement.

When operated at 4 MHz, the dimensions of such a unit is on the order of50.4″×28″×10″. For most mobile and aircraft applications, this footprintis double the desired size. As described above, what was needed was abreakthrough which would reduce the size of the footprint in half suchthat one embodiment with the subject top shield to be described, thefootprint is now 36″×20″×5″. The reduction in size over the standardmeander line loaded antenna is a result of the top shield over such astructure.

As will be seen in FIGS. 8A and 8B sections of alternating impedancerelative to the conductor plate are provided with a top shield thatlowers the operating frequency of the associated meander line. It doesso by affecting the propagation constant of the meander line structure.The propagation constant relies on the number of high impedance/lowimpedance transitions per unit length. This characteristic is a resultof the fact that each transition causes a fixed phase shift. The morephase shifts per unit length, the more delays per unit length. Whenutilizing the subject top shield connected to the conductor plate, thereare more phase shifts per unit length and therefore more delays per unitlength. This double-sided structure, thus, has double the number oftransitions per unit length such that more delay is accrued.

As will be seen in FIGS. 9 and 10, when utilizing the top shield thehigh impedance sections are now the vertical segments of the meanderlines. The horizontal sections therefore constitute the low impedancesections. The net result is that for the same footprint for the standardmeander line structure, its effective length is doubled meaning that itcan resonate at a lower cutoff frequency.

Referring now to FIG. 8A, in one embodiment such a meander linestructure includes a top section 240 connected via a vertical section242, in turn connected to a lower section 244 which is in turn connectedvia a conductive strip 246 to a bottom conductive plate 248. The meanderline is fed via an upstanding plate 250 connected to a signal source 251such that the signal is applied between ground and plate 250 to section240 of the meander line. A top shield 252 is connected by an upstandingsegment 254 to horizontal conductive plate 248, the effects of whichwill be described hereinafter.

Schematically and referring to FIG. 8B, top section 240 is connected bysection 242 to lower section 244, which is in turn connected viaconductive strip 246 to conductive plate 248 as illustrated. Plate 248is connected via upstanding conductor 254 to shield 252 as illustrated,with the feed for the meander line structure being via upstanding plate250 fed by signal source 251.

Referring now to FIG. 9A, the diagram shows the relative impedances forthe upper and lower sections of the meander line relative to conductorplate 248. Here it will be seen that the horizontally running uppersection 240 is at a high impedance, whereas the lower section 244 is ata lower impedance. For extended meander line structures there is analternation of high impedance and low impedance sections, with thenumber of sections being determined by the particular application.

Referring to FIG. 9B, it can be seen that if the frequency of a meanderline structure is to be changed, various sections may be switched intoand out of the meander line. Here a switch 260 is interposed in theupstanding portion 242 which connects upper section 240 with lowersection 244.

What will be seen is that the switch connects a high impedance sectionto a low impedance section. When the switch is open, there issignificant voltage stress on the switch that may be from between 5,000and 10,000 volts.

Here, if one wished to transmit 100 watts of power, then such aswitching system could possibly be designed to tolerate the voltagestress. However, if one wanted then to increase the power of thetransmitter from 100 watts to 300 watts, this could conceivably exceedthe allowable voltage stress on the switch.

Referring to FIG. 10A, if the structure of FIG. 9A were provided withtop shield 252, then the result would be as follows:

Top section 240 would become a low impedance section, whereas upstandingsection 242 would become the high impedance section. This high impedancesection would then be connected to low impedance section 244 and so on.

What will be seen is that the relative impedances of the varioussections of the meander line are altered with the use of a top shield.In a given length transmission line there would be double the number ofhigh impedance/low impedance transitions when using the top shield.

Moreover, as illustrated in FIG. 10B switch 260 now connects a lowimpedance section 240 to another low impedance section 244 such that thevoltage stress across switch 260 is minimized.

What this means is that when using a top shield there is considerablyless voltage stress on the switches. This in turns translates into beingable to handle increased output power from a transmitter.

Referring to FIG. 11, a slow wave meander line structure may include anumber of sections 260, 262, 264, 266 and 268 which sections areconnected together in general in the same manner as illustrated inconnection with FIG. 7. When this device is utilized as an antennacoupler, grounded loop antenna 234 may be connected as illustrated.

Referring to FIG. 12, when the structure of FIG. 11 is provided with atop shield 270, new characteristics make possible a lower cutofffrequency for the structure such that for a given size structure a lowercutoff frequency can mean the difference between communications andcommunications failure as will described in connection with FIG. 13.

As can be seen in FIG. 13, one operative embodiment of the subjectinvention involves a mounting of an antenna and coupler to a vehicle271. Vehicle 271 carries a transmitter connected to the coupler. Thepurpose of utilizing the shielded embodiment of the coupler is such asto be able to establish communication between vehicle 271 and anothervehicle 272 at some distance from vehicle 271.

Without the shield, a reasonably sized coupler and antenna can only bemade to operate as low as 5 MHz. The result of the utilization of a 5MHz carrier is that the takeoff angle 274 is shallow. This means thatwhen radiation as illustrated at 276 is reflected by ionospheric layer278, its point of impingement on the surface of the earth 279 is waybeyond vehicle 272. In essence there is a skip-induced dead zone, thelength of which is determined by the operating frequency of thetransmitter.

If on the other hand utilizing the same sized coupler and antenna onecould transmit at 4 MHz, then radiation as illustrated at 280 would beprojected upwardly at a takeoff angle 282 which would result incommunications with vehicle 272 at, for instance, a distance of 30+miles. From a practical and tactical operational view point,communications between vehicle 271 and vehicle 272 can be achievedthrough the ground wave which dissipates at approximately 30 miles fromthe transmission source. The ground wave coverage is illustrated at 84.Skip or sky wave coverage then exists from 30 miles up to 100 miles.

What is accomplished by the utilization of a shielded meander linecoupler is to provide a compact unit which can be vehicle-mounted andcan establish communications from the transmit site by ground wave up to30 miles and then by sky wave from 30 to 100 miles, thus eliminating thedead zone associated with operating at 5 MHz instead of 4 MHz. As can beseen, the dead zone at 5 MHz is illustrated by double ended arrow 290,whereas for 4 MHz the dead zone is illustrated by double ended arrow292.

What can be seen is that by utilization of the shielded meander linestructure, one can lower the low frequency cutoff of the coupler andantenna while at the same time providing for robust frequency shiftingor switching at ever increasing transmit powers.

The subject shield meander line structure also has application in the 30MHz–88 MHz range in which frequency hopping is utilized for covertoperation.

Referring to FIG. 14, what is shown is a VSWR graph versus frequencywhich indicates by line 300 that the cutoff frequency for a suitablysized meander line structure is on the order of 45 MHz. However, withthe shielded meander line structure, as illustrated by line 302 the VSWRis at a very acceptable 2:1 at 30 MHz. In this embodiment the meanderline structure is indeed a broadband device which operates criticallydown to the 30 MHz lower end of this particular band.

As illustrated in FIG. 15, a suitable meander line loaded antenna can beconstrued in a volume 32″×32″×10″, whereas without the subject topshield, the meander line structure would have to be enlarged by double,unacceptable for mounting on aircraft or ground based vehicles.

The top shielded meander line structure is also of significant advantagewhen wide band antennas are to be utilized in wireless handsets.

Referring now to FIG. 16A, a meander line loaded antenna is constructedfrom the aforementioned top section 240, upstanding section 242, lowersection 244, conductor 246 and conductive plate 248, with top shield 252being connected to plate 248 by upstanding member 254. The antenna isfed by a vertical conductive plate 250 as described above fed by signalsource 251. The structure thus described is filled with dielectricmaterial 310, with a capacitive fine adjustment plate 312 beingpositioned as illustrated.

The utilization of a wide band meander line loaded antenna for wirelesshand held units achieves the benefit of compact size, in one embodiment1.2″×1.2″×0.3″, with a relatively low VSWR across not only the cellularband, and the PCS band as well as the GPS band, but also out to 6 GHz.

How this is accomplished is through the utilization of the meander linetechniques described above in combination with the ability to lower thelow frequency cutoff of the meander line loaded antenna. Were it not forthe top shielding, the lowest frequency at which the antenna wouldradiate would be approximately 1750 MHz. This is clearly above thepopular cellular band at 800 MHz.

By providing the top shield, the low cutoff frequency of the antenna isdrastically reduced, which can be seen by the graph of FIG. 16B. Here,the VSWR is 2:1 at 780 MHz. As can be seen by line 320 the low frequencycutoff of such a wireless handset antenna in one instance is around 1750MHz. However, by utilizing the shield, as illustrated by line 322, theVSWR can be maintained below 2:1 at 800 MHz.

Thus a compact wide bandwidth antenna is now available for handheld usein which the antenna may be embedded into the handheld unit.

There is, however, an unusual result when utilizing the shielded meanderline structure. As illustrated in FIG. 17 a standard handset 330 with aninternal antenna has an antenna lobe 332 which looks like half a dipole.This is true for 800 MHz operation. However, and referring now to FIG.18, for 1.9 gigahertz operation at PCS frequencies, the main lobe 332 isnarrowed and points downwardly which is referred to as “down firing”.This is due to the ground plane effect of the circuits within the cellphone and is directly related to the ground plane or planes utilized inthe printed circuit board or boards within the cell phone.

Referring to FIG. 19, if handset 330 were to be provided with a wideband meander line antenna 340, then at 800 MHz the major antenna lobewould be a dipole type lobe 342.

Referring to FIG. 20, were this handset operated in the 1.9 GHz region,the main lobe 342 while somewhat narrow would still be in the horizontaldirection, thus eliminating the ground plane effect associated with theFIG. 18 embodiment.

What can be seen is that a compact wideband wireless handset and antennacan be achieved with a low cutoff frequency including all the bands ofinterest through the utilization of the top shield. Moreover, theutilization of the top shield in combination with the meander lineloaded antenna provides the desirable horizontal lobe and eliminatesdown firing.

While the present invention has been described in connection with thepreferred embodiments of the various figures, it is to be understoodthat other similar embodiments may be used or modifications or additionsmay be made to the described embodiment for performing the same functionof the present invention without deviating therefrom. Therefore, thepresent invention should not be limited to any single embodiment, butrather construed in breadth and scope in accordance with the recitationof the appended claims.

1. An antenna tuner for coupling an antenna to a signal source so as tomatch the antenna input impedance to the transmission line between thesignal source and the antenna, comprising: a variable length meanderline coupled to said antenna and said transmission line source; and,means for varying said meander line length until the antenna inputimpedance matches that of said transmission line.
 2. The antenna tunerof claim 1, wherein said meander line includes a number of sections andwherein said means for varying said meander line length includes atleast one switch connected between said meander line sections.
 3. Theantenna tuner of claim 2, wherein said switch shorts a portion of onemeander line section to a portion of another meander line section. 4.The antenna tuner of claim 2, wherein said switch connects one meanderline section to another meander line section.
 5. The antenna tuner ofclaim 2, wherein said switch is a solid state switch.
 6. The antennatuner of claim 5, wherein said solid state switch includes a PIN diode.7. The antenna tuner of claim 1, wherein said meander line includes anumber of folded sections, one end of said meander line coupled to saidtransmission line and wherein said antenna includes a monopole antennahaving a free end and an opposite end coupled to the other end of saidmeander line.
 8. The antenna tuner of claim 1, wherein said meander lineincludes a number of folded sections, one end of said meander linecoupled to said signal source, and wherein said antenna includes a loopantenna having one end grounded and an opposite end coupled to the endof said meander line coupled to said transmission line.
 9. A method ofmatching the impedance of an arbitrary antenna to the impedance of atransmission line, comprising the steps of: providing a variable lengthmeander line having one portion coupled to the antenna and one endcoupled to the transmission line such that the impedance of the antennais in parallel with the impedance of the meander line; and, varying thelength of the variable length meander line to function as a tuner untilthe impedance of the meander line and antenna matches the impedance ofthe transmission line.
 10. The method of claim 9, wherein the meanderline includes a number of sections and wherein the step of varying thelength of the meander line includes the step of selectivelyinterconnecting sections of the meander line.
 11. The method of claim10, wherein the step of selectively interconnecting sections of themeander line includes shorting out portions of different sections of themeander line.
 12. The method of claim 10, wherein the step ofselectively interconnecting sections of the meander line includesconnecting together different meander line sections.
 13. The method ofclaim 10, wherein the selective interconnecting step includesinterconnecting different meander line sections at a high impedancenode.
 14. The method of claim 13, wherein the step of interconnectingdifferent meander line sections at a high impedance node includes asolid state switch, whereby the load-carrying capabilities of the solidstate switch can be minimized.
 15. A method for providing a high gainantenna tuner, comprising the step of utilizing a variable lengthmeander line as a lumped element antenna tuner, wherein the meander linetuner includes a solid state switch for interconnecting various meanderline sections, whereby losses across the switch are minimized ascompared to losses associated with solid state switches used in lumpedelement antenna tuners.
 16. A method of providing a slow wave meanderline with a lowered low-frequency cutoff, the meander line having aconductor plate and sections of alternating impedance relative to theconduction plate, comprising the step of: providing a top shield overall of the meander line components, the top shield being electricallycoupled to the conductor plate of the meander line and providing alowered resonant frequency.
 17. A meander line loaded antennacomprising: a separate antenna; a meander line having a conductor platecoupled to said antenna, and, a conductive shield over the top of thecomponents of the meander line and electrically connected to saidconductor plate, whereby the low frequency cutoff of said antenna islowered.
 18. A meander line having a reduced low frequency cutoff,comprising: a meander line structure having a top section, anintermediate section, a bottom section, and a bottom electricallyconductive element, and a shield over substantially all of said meanderline structure and electrically connected to said bottom element.
 19. Aslow wave meander line having a conductor plate and sections ofalternating impedances adjacent said conductor plate and a top shieldconnected to said conductor plate and positioned over substantially allof said sections of alternating impedances, said top shield lowering theresonant frequency of said meander line, whereby said meander line whencoupled to a separate narrow band antenna lowers the resonant frequencyof said narrow band antenna and when coupled to a separate wide bandantenna lowers the low frequency cut off of said wide band antenna. 20.The meander line of claim 19, wherein said meander line has a number ofsections creating a number of phase shifts and wherein said top shieldincreases the number of phase shifts associated with said meander linesections, thus creating more meander line delay.
 21. The meander line ofclaim 19, and further including a separate antenna coupled thereto, saidmeander line functioning as an antenna tuner.
 22. The meander line ofclaim 21, wherein said antenna has a distal end and wherein said distalend is grounded.
 23. A method for eliminating down firing of an antennacarried by a wireless handset, comprising the step of embedding in thehandset a slow wave meander line having a conductor plate, a top shieldcoupled to the connector plate, and a separate antenna coupled to themeander line.
 24. The method of claim 23, wherein the antenna is a wideband antenna.
 25. The method of claim 24, wherein the antenna operatesabove 1.7 gigahertz and eliminates down firing above the 1.7 gigahertzfrequency.
 26. An antenna for use in the 30 to 80 megahertz band,comprising: a wide band slow wave meander line antenna having aconductor plate and a low frequency cutoff below 30 megahertz, whereinsaid meander line antenna includes a top shield electrically connectedto the conductor plate thereof, said shield responsible for the loweringof the low frequency cutoff of said wideband antenna.
 27. A method forreducing voltage stress in a frequency-switched meander line having aconductor plate, high-impedance horizontal sections, low-impedanceupstanding vertical sections between two adjacent high-impedancehorizontal sections, and a switch interposed in an upstanding section ofthe meander line between two adjacent horizontal sections, comprisingthe step of providing a top shield for the meander line oversubstantially all of the meander line sections and connected to theconductor plate thereof, whereby, with the shield in place, the topshield converts high impedance horizontal sections to low impedancesections, and the low impedance section to a high impedance section, theswitch being in the high impedance section between the low impedancesections.